Blake E. Humphers pleaded not guilty Tuesday in Multnomah County Circuit Court to robbery, attempted murder, attempted assault and unlawful use of a weapon charges. An anonymous tip to police led to Humphers' arrest in Gresham on Oct. 26, said Sgt. Pete Simpson, a Portland Police Bureau spokesman. Humphers was booked into the Multnomah County Detention Center the next day.

Humphers allegedly approached Joshua J. Smith, 28, Sept. 13 on a MAX platform at Southeast Foster Road near Interstate 205 and told Smith he wanted to listen to his headphones, police said. When Smith said no, Humphers reportedly pulled out a handgun and fired towards Smith.

The two then got into a scuffle and Humphers eventually fled on a bike, police said. Smith injured his arm in the scuffle, but wasn't hit by gunfire. Humphers accidentally shot himself in the leg, Simpson said. No one else was reported hurt.